The invention relates to a method for drilling geothermal wells whereby the raw steam produced is treated with ferric chelates to remove substantially all of the hydrogen sulfide gas contained therein.
Geothermal steam wells are drilled with compressed air as the motive force for the drill bit. Due to the high temperatures encountered and highly fractured nature of the reservoirs, drilling mud is not an option. As the drilling enters steam producing areas, the air and steam escape through the casing into a blooie line and muffler. The stringent air pollution standards require that the H.sub.2 S in the steam be abated.
Once a well is completed, a flow test is performed. A flow test consists of opening the well full bore and letting it blow through the blooie line. It is during this period that a majority of the need for H.sub.2 S abatement occurs. These flow tests last from 30 up to 90 days depending on the experience with the reservoir.
Once wells are in production, they tend to foul as a result of the impurities present in the steam. Eventually, production will drop off and reworking of the well is necessary. Reworking involves bringing a rig in and drilling deeper into another steam producing zone or widening the bore. Again, H.sub.2 S abatement is necessary. As they reach an area of steam production, the well is again flow tested. The flow test at this point is much less, from 15 to 30 days. Generally, H.sub.2 S abatement requirements are about half that of a new well.
It is known from U.S. Pat. No. 4,151,260 that H.sub.2 S gases contained in steam can be abated during the drilling of geothermal wells by treating the steam with an alkaline solution of hydrogen peroxide.
The use of iron chelates to treat exhaust geothermal steam from a steam turbine is taught in U.S. Pat. No. 4,414,817.
It is known from Ser. No. 748,292 filed June 24, 1985 that cationic polymeric catalysts are useful to accelerate the oxidation of H.sub.2 S with iron chelates in exhaust steam from geothermal power plants.